First Day Lessons
by wolveswolvesandmorewolves
Summary: Clary, Alec, Isabelle, and Jace are all at the Institute, waiting for the teacher to walk in so they can finally begin their first day learning more about demons. But what happens when the new teacher decides to teach them in a new way? Oneshot. Crossover between Infernal Devices and Mortal Instruments.


** So the following is a little cross-over of Mortal Instruments and Infernal Devices. This just popped into my head the other day. After City of Fallen Souls and after Clockwork Princess. **

** Review!**

** -Lilith**

** Clary's POV**

I was so screwed.

Running through the halls of the Institute, I wondered how late I was. Jace, Alec, and Isabelle were probably there already, so I was going to be the last one to arrive. Running into the elevator, I pushed the button and then the 'close doors' button over and over again, hoping to speed up the old elevator.

"Come on, come on." I muttered under my breath, swinging my red hair over my shoulders. As the elevator started with a creaky groan, I tied my hair up into a messy ponytail, sweeping my long red locks up into a handful and tying it off, keeping it off my shoulders and down my back instead. The soft feeling of my hair was comforting, soothing. It calmed my nerves just a tad before they started up again.

Today wasn't going so well. I had woken up late, pretty much throwing a wrench into my whole plan of not showing up behind schedule. I had hastily thrown on some gear and had barely swallowed down coffee before dashing out the door, hurrying to the Institute.

I remembered vaguely where to go, which halls that looked familiar and which doors to take. Locking the directions on my head, I stumbled out the elevator and ran down the hall, my feet thumping softly on the carpet. Making my way through the winding halls that were slowly starting to look familiar, I stopped in front of a wooden door. No sign, no windows so I could look in. No way of identification, just a blank looking door.

Praying that I hadn't found the wrong door, I swung it open. At first I had thought that I had stumbled through a portal to some high school, since it looked exactly like a classroom. A blank whiteboard at the front, empty desks with words engraved into them, white tiled floors. A mahogany desk sat at the front, empty accept for a few books that sat on the front desk. The desks looked worn and aged from years of students sitting there. Empty accept for a few.

Alec, Isabelle, and Jace all sat in the back, ignoring me. Alec and Isabelle were on their phones, not bothering to look up as I examined them. Jace just started forward, eyes blank, lost in thought. His eyes snapped to mine when I opened the door.

"You're late." Alec hissed, and I looked around before finally spotting a clock mounted on the wall. Sure enough, it was three minutes past ten.

"Not my fault the elevator is slow." I hissed back, then sat beside Isabelle. She didn't look up from the screen as I sat there, not knowing if to start a conversation or not. Probably not. Isabelle wasn't my favorite female Shadowhunter, and seemed to be unpredictable at times. Best not tick her off this early in the morning.

Suddenly, my phone vibrated in my pocket. Looking around, I realized that there really wasn't a need to be secret, since both Alec and Isabelle had their phones out. Sliding it out, I slid my finger across the screen and tapped in my code. A text from Jace.

**Where were you?**

Sighing, I tapped the screen, accessing the key pad. Jace had seen right through me, of course. It wasn't a real big deal though.

_I woke up late._

A few seconds later, I heard the soft buzzing of his phone vibrating from the other side of the room. I watched him as he pulled it out and then read the text before typing up a reply. Turning my gaze back to my phone, I read his new message.

**Just be glad the new teacher isn't here. She would probably have a cow if she caught you.**

Snorting, I hit the reply button and let my fingers fly, hitting letters that popped up in the text box. After I was sure I was done, I hit the reply button and sent it to him.

_Thank the Angel for that. What are you thinking about? _

His face didn't change as he replied.

**Where this teacher is. It's almost a quarter after 10. She should be here by now.**

Glancing up at the clock, I realized that he was right: it was 10:14.

_Maybe she was late too. Or just didn't want to get out of bed._

He chuckled darkly at that, then replied.

**I say we give her an hour before leaving. If she's not here by then I am gone. **

I agreed with him. I didn't want to be here as much as he did, even if we were going to learn more about demons. Mondays were the bane of my existence.

_Let's do it._

He didn't text me anymore after that. Alec had snapped at him, getting annoyed since Jace's phone kept vibrating, and told him to stop. He probably didn't have much more to say anyway.

Soon another fourteen minutes passed, then another. By then I had taken out my emergency notepad and pencil, knowing that 18 minutes wasn't really enough time to cover more information about demons. Isabelle had given up too and was playing Angry Birds on her phone, her perfectly manicured nails clicking against the screen as she directed the virtual birds.

Humming softly under my breath, I lightly began to sketch Church. When I was bored, I often just drew things that came to my mind, and drawing the Institute seemed too much of a challenge. But Church was a much better subject.

I was shading in his fur when the door was suddenly thrown open. Isabelle ran inside, wearing gear and her hair up in a bun.

"Sorry I'm late guys. My alarm didn't go off." She gasped, slightly breathing heavy.

I stared at the girl beside me, who was watching the new Isabelle with interest. The Isabelle who had just run into the room paused, looking up when she didn't hear anybody speak. Following all of our gazes, she stared at her mirror image and froze. Straightening up in a flash, she pulled the knife out of her hair, which had been holding up her bun, letting her long inky black waves of hair fall down her back.

"Who are you?" She asked, and I could hear the dangerous steel in her voice.

Instead of replying, the other Isabelle put up her phone and stood up. There was a soft pop, and then there was a different girl standing in Isabelle's place. A girl with long brown hair, curly and elegant, with pale creamy skin. Her eyes were a strange grey, cool and reserved. She was a little bit taller than Isabelle, and I could see an aura of quiet power around her. Her body was unmarked, smooth and without a blemish. She didn't have any Marks, no proof that she was a Shadowhunter except for her gear.

She smiled, her eyes flashing. "I am Tessa, your new teacher. Now, since I believe that I have taught you something valuable today, class dismissed."

We all stared at her for a minute, trying to process what had just happened. Jace broke out of his trance first. "Well, I'm out of here." He announced, then walked out the room, the rest of us slowly following, still in shock.

Jace was waiting for me when I got outside. "What just happened?" I asked, and he shrugged.

"I believe that we have learned about a type of demons." He replied.

"What kind is that?"

"Shape shifting."

** That just popped in my head the other day. I'm not going to do any more Mortal Instruments fanfics since I can't read the next book until I'm older. **

** So you like? Hate? Average? Review!**

** -Lilith**


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